Rendering partials / view in a rake task / background job / model in Rails 4

ruby, ruby-on-rails, ruby-on-rails-4

Solution

Here's what I compiled from lots of sources and what works for me in Rails 4.

With this Renderer class, you should be able to render Rails 4 views and partials in any context, like background jobs, service objects, models, workers, you name it.

# app/services/renderer.rb
# Render views and partials in rake tasks,
# background workers, service objects and more
#
# Use:
#
# class MyService
#   def render_stuff
#     result = renderer.render(partial: 'tweets/tweet', locals: {tweet: Tweet.first})
#     # or even
#     result = renderer.render(Tweet.first)
#   end
#
#   private
#
#   def renderer
#     @renderer ||= Renderer.new.renderer
#   end
# end
#
class Renderer
  def renderer
    controller = ApplicationController.new
    controller.request = ActionDispatch::TestRequest.new
    ViewRenderer.new(Rails.root.join('app', 'views'), {}, controller)
  end
end

# app/services/view_renderer.rb
# A helper class for Renderer
class ViewRenderer < ActionView::Base
  include Rails.application.routes.url_helpers
  include ApplicationHelper

  def default_url_options
     {host: Rails.application.routes.default_url_options[:host]}
  end
end

Update:

There seems to be an easier solution: http://makandracards.com/makandra/17751-render-a-view-from-a-model-in-rails

ApplicationController.new.render_to_string(
  :template => 'users/index',
  :locals => { :@users => @users }
)
# Mind the weird syntax to set @ variables in :locals.

Update 2:

There's a gem called `render_anywhere` that allows for calling "render" from anywhere: models, background jobs, rake tasks, etc.

Update 3:

In Rails 5, the renderer has been extracted and can be used standalone from background jobs and other places:

ApplicationController.renderer.render(
  partial: 'messages/message',
  locals: { message: message }
)

For Rails <= 4.2, this functionality can be backported with the backport_new_renderer gem.

Problem

Original source